Known marine propellers, especially those designed for use with power sources, such as internal-combustion engines of relatively high horsepower, are mainly metallic or, if of non-metallic material, utilize metallic inserts for increased strength, principally in the form of a metallic hub having splines to receive the driving shaft. Moreover, prior propellers, in order to further achieve the requisite strength, have thick heavy spokes between the hub and the surrounding barrel, which reduces the open area for the passage and evacuation of engine exhaust gases. The use of metallic hubs elevates the load level at which the hub or shaft splines will shear in response to overloads, often resulting in extreme and costly damage to the power transmission. Still, further, prior propellers have been costly and complicated to manufacture.
According to the present invention, the foregoing disadvantages and drawbacks are eliminated and a significantly improved, high-strength, lower-cost and markedly more efficient product is provided, featuring such improvements as one-piece construction, of strong, light-weight material, which in one embodiment is non-metallic material of the class including polyester; a barrel or nave structure configured as an interior screw for facilitating the discharge or evacuation of exhaust gases from the driving engine; and the provision of a hub having internal key means designed to shear in response to overloads on the propeller of a predetrmined value below the level at which the power transmission would be damaged. Other aspects of the invention reside in materially lower cost of manufacture, long life and more efficient operation.
Further features will become apparent as preferred embodiments of the invention are disclosed herein.